1. Field of the Invention
The present invention relates to an actuator assembly having a magnetoresistive head (MR head), and a magnetic disk drive including the actuator assembly.
2. Description of the Related Art
In response to recent downsizing and density increasing of a magnetic disk drive, the flying height of a head slider has been reduced and it has been desired to realize contact recording/reproduction such that the slider flies at a very short height from a recording medium or comes to contact with the recording medium. In a conventional magnetic induction head, a decrease in peripheral speed (relative speed between the head and the recording medium) due to a decrease in diameter of a magnetic disk causes a deterioration in reproductive output. It has therefore been desired to develop a magnetoresistive head (which will be hereinafter referred to simply as MR head) which can obtain a large reproductive output even at a low peripheral speed with no peripheral speed dependence of reproductive output.
In the MR head, a constant sense current is supplied to a magnetoresistive element (MR element) to convert changes in magnitude of a signal field leaking from a recording track of the recording medium into changes in resistance, thereby reproducing the information recorded on the medium as changes in voltage. The MR element of the MR head or head slider is formed generally by a thin-film process or the like. The head slider further has a coil for writing data to the recording medium. The head slider is mounted by adhesion or the like on a front end portion of a suspension formed of stainless steel.
Lead lines for connecting the MR element and the coil to a recording and reproducing circuit in a magnetic disk drive are formed by copper patterns printed on the suspension. By mounting the suspension on a front end portion of an actuator arm, the MR element and the coil are connected through a flexible printed circuit board (FPC) or the like to the recording and reproducing circuit. In the suspension for supporting a conventional MR head slider, a pair of lead lines connected to the terminals of the MR element are electrically open, or the head lines and a ground line connected to a magnetic shield for the MR element are electrically open. Further, since the electrostatic breakdown voltage between the terminals of the MR head is low, the MR head is limited in handling more than a conventional monolithic head.
Accordingly, when a worker charged with static electricity handles such a suspension having the MR head slider or carries the suspension contained in a static-prone plastic case or the like, an excess current due to the static electricity flows into the MR element to burn the MR element, or the static electricity is discharged between the MR element and the magnetic shield to cause burning of the MR element. In other words, if a voltage of several volts to tens of volts is applied between the terminals of the MR element, between the terminals of the MR element and the head slider, or between the terminals of the coil and the head slider, the MR element may be broken by static electricity, causing a damage to the function of the head.
To cope with this problem various related objects including tools for use in fabrication, head mounting, terminal soldering, etc., working desks, working clothes, and storage shelves are formed of low-static voltage materials. Further, metal portions of the objects are grounded in consideration of safety to avoid charging or electric shock. In addition, an ionizer is used to always remove static electricity from the hand of the worker, for example.
However, the following problems yet remain although the above measures have been taken.
a) The static electricity generated in a human body working with clothes differs according to individuals, and there is a possibility that the static voltage may easily reach a head breakdown voltage.
b) An impedance to the ground cannot be set so low from the safety standpoint against electric shock, so that a margin between an electricity removable potential and a head breakdown voltage is narrow.
Thus, it is very difficult to completely eliminate defective MR heads broken in fabrication, head mounting, terminal soldering, etc.